The present invention relates to the technology effectively applied to a high frequency power amplifier circuit that amplifies and outputs high-frequency signals. More specifically, the present invention relates to the technology effectively applied to an open-loop high frequency power amplifier circuit that controls an amplifying transistor's operating power supply voltage (power supply voltage) in accordance with output request levels to control output power. For example, the present invention relates to the technology effectively utilized for a high frequency power amplifier circuit used for cellular phones and electronic parts (power modules) including that circuit.
Generally, the transmitting output portion in a radio communication apparatus (mobile communication apparatus) such as a cellular phone is provided with a high frequency power amplifier circuit (power amplifier) to amplify modulated transmission signals. A conventional radio communication apparatus uses an APC (Automatic Power Control) circuit to control the high frequency power amplifier circuit's gain in accordance with transmission request levels supplied from a base station. The APC circuit detects an output power from the high frequency power amplifier circuit or an antenna and generates a transmission output control signal based on the detected signal and an output level designation signal from a baseband circuit and the like. The conventional radio communication apparatus is configured to control bias voltages for the high frequency power amplifier circuit so that a control voltage output from the APC circuit provides an output power needed for conversation (e.g., see patent document 1)
Conventional communication systems for cellular phones include GSM (Global System for Mobile Communication). The GSM system uses a phase modulation system called GMSK (Gaussian Minimum Shift Keying) that shifts carrier wave phases in accordance with transmission data. The GSM-based communication system only needs to amplify and output phase-modulated signals in accordance with requested output levels. Generally, a GSM-based cellular phone generally fixes the input signal amplitude, allows a bias circuit to control idle currents for amplifying devices in the high frequency power amplifier circuit in accordance with request output levels, and feedback controls the output power. This control system is generally referred to as the closed-loop system.
However, the APC circuit needs to be provided for the output power control system according to the above-mentioned closed-loop system. Provision of the APC circuit increases the circuit scale and decreases the packaging density. To solve this problem, there is disclosed the system (e.g., see patent document 2) that controls an operating power supply voltage (power supply voltage) of the amplifying device (power FET) so that an output level varies based on and in proportion to a signal that designates the output level. In this manner, the system linearly operates the amplifying device to ensure linearity of outputs from the high frequency power amplifier circuit. This system is called the open-loop system and provides an advantage of providing a smaller circuit scale that the closed-loop system.
Japanese Unexamined Patent Publication No. 2000-151310
Japanese Unexamined Patent Publication No. 2003-243994